WATER HARVESTING AND INFILTRATION IN ARID AREAS AFFECTED BY SURFACE CRUST - EXAMPLES FROM JORDAN

In arid and semi-arid areas, surface runoff occurs at low rainfall int ensities due to the presence of the surface crust. Variation in surfac e runoff can be attributed to the variation in rainfall amount and int ensity, soil water content, infiltration, and watershed size and slope . Three micro-watersheds were selected within Muwaqar region to invest igate runoff-rainfall characteristics and infiltration in soils affect ed by surface crust. The sites were selected to represent different si zes and slopes with well defined outlets or wadis. Flood measurements were carried out using rectangular sharp-crest contracted weirs and a Steven-water height recorder to record water height above the crest we ir. In arid areas affected by surface crusts, increasing watershed siz e increased total volume of runoff water and decreased both volume of runoff water per unit area and runoff coefficient owing to the fact th at increasing watershed size increased infiltration, evaporation and d epression storage losses. Owing to reduction in infiltration, evaporat ion and depression storage losses as the slope of the watershed increa ses, increasing watershed slope increased total volume of runoff water , volume of runoff water per unit area and runoff coefficient. Rainwat er harvesting works best on sloped soil with a surface crust that has a low infiltration rate. This indicates the potential for rainwater ha rvesting when topography and soil conditions are favourable. (C) 1997 Academic Press Limited.